1. Field of the Invention
The present invention relates to an overcurrent protection circuit. More particularly, it relates to an overcurrent protection circuit which can be introduced into a battery feed circuit for line circuits in a switching system.
As is well known, an overcurrent protection circuit protects a circuit from abnormally large currents, for example, a load current flowing through the circuit abnormally larger than a rated current therefor. The most typical means for protecting a circuit from abnormally large current is a fuse. A fuse is blown by large currents due to, for example, short-circuits, thereby protecting the circuit from damage. Various other types of overcurrent protection circuits have been proposed and put into practical use.
2. Description of the Related Art
Overcurrent protection circuits can be basically classified into two types: fusible types and semiconductor types. An overcurrent protection circuit of the latter type, i.e., the semiconductor type, is fabricated with transistors. Known transistor-type overcurrent protection circuits offer dual protection against large currents, first by limiting the current and second by breaking the current.
However, there are problems in prior art overcurrent protection circuits. Transistor-type circuits inevitably consume power and it is difficult to fabricate compact transistor type circuits inexpensively since they must withstand the heat caused by short-circuits. Fusible type circuits must be replaced each time a short-circuit occurs. This means that many fuses must be stocked. Further, a window must be provided to allow determination of the fuse state. Furthermore, the overall design of the equipment must be such as to allow easy replacement of fuses.